Various types of heaters have been proposed over the years for heating fluids. Most, if not all, employ a heat exchanger disposed proximate a source of heat through which the fluid to be heated passes. For example, residential heating systems employing water-filled radiators typically have a furnace unit wherein a combustible, such as natural gas, is burned in a combustion chamber. In gas furnaces, the combustible is burned by a burner unit which may include a plurality of elongated tubes with openings along an upper extent thereof for distributing a mixture of air and gas along the length of the tube for burning as it exits the openings. In this manner, the surface area over which combustion takes place is matched to the general surface area profile presented by a heat exchanger unit.
A heat exchanger in the form of a metal conduit through which the water to be heated may pass is positioned above the burning gas in order to absorb the heat of combustion and conduct it to the water passing through the conduit. To increase the efficiency of heat transfer, the heat exchanger is configured to maximize exterior surface area exposed to the heat of combustion, as well as the internal surface area in contact with the water. Many heat exchangers utilize metal fins on the conduit for this purpose. One of the more common forms of heat exchanger is the traditional, parallel tube heat exchanger wherein a plurality of tubes passing over the combustion chamber of a heater communicate with manifolds at either end. The flow through the conduit is circuitous, passing back and forth through the tubes from one manifold to the other gathering heat from the combustion chamber and exiting from an outlet port on one of the manifolds to supply a heated fluid, e.g., to a radiator system. The same type of heat exchanger has been employed for heating the water in swimming pools and for other fluid heating purposes.
Many variations on the above described heat exchanger have been proposed for the purpose of increasing efficiency, lowering the costs of production and otherwise improving existing heater designs. For example, U.S. Pat. No. 5,178,124 to Lu et al. discloses a hot air heater with a heat exchanger having a primary portion composed of a plurality of "S" shaped metal tubes which receive the products of combustion that are ultimately vented to the atmosphere. A plastic heat exchanger having a plurality of tubes or channels that communicate at ends thereof with first and second manifolds receives the combustion products from the "S" shaped tubes after the gases have lost sufficient heat so as not to constitute a threat of melting to the plastic heat exchanger. This configuration differs from the previously described fluid heaters, in that the pathways for the products of combustion and the heat transfer medium are interchanged, i.e., the combustion products rather than the transfer medium are directed through the interior conduit of the heat exchanger.
Heat exchangers, per se, have diverse applications, e.g., for use as radiators for cooling internal combustion engines. In U.S. Pat. No. 5,305,826 to Couetoux, a radiator configuration is disclosed wherein a header manifold has a temperature responsive double-acting valve for controlling the flow through the radiator. A first valve portion restricts flow through the entire radiator while a second portion interacting with an aperture in a manifold divider bulkhead permits fluid to exit the radiator without passing through the core. In this manner, the temperature responsive valve performs a thermostatic control function for altering the cooling efficiency of the heat exchanger in response to cooling requirements.
Plastic is a corrosion-resistant, light and economical material that has wide application for manufactured goods. In recent years it has been recognized that some heat-resistant plastics can be used for heat exchangers or parts thereof in certain applications. For example, U.S. Pat. No. 3,628,603 to Fieni discloses an automobile radiator having header tanks formed from molded plastic. U.S. Pat. No. 3,489,209 to H. G. Johnson relates to a heat exchanger having plastic and metal components and U.S. Pat. No. 4,290,413 to Goodman et al. discloses a solar energy collector formed from plastic. U.S. Pat. No. 5,216,743 to Seitz discloses a thermoplastic heat exchanger used for heating fluids via a pair of electric heating elements that are inserted within the body of the plastic heat exchanger.
While plastic components and plastic heat exchangers have been utilized in low heat transfer applications, such as in an automobile radiator where heated water is cooled by contact with the air and/or in a solar collector where water is heated by exposure to sunlight, plastic has typically not been utilized in applications where the plastic component is exposed to the direct heat of combustion and/or high pressures. In those conditions, even heat-resistant plastics are subject to weakening and deformation.
In addition to the efforts to improve the composition of heat exchangers to produce more economical and reliable products, heat exchanger designers have sought to improve the tube sheets and the tube sheet-to-tube connections to provide lightweight heat exchangers with good integrity. It was recognized, for example in U.S. Pat. No. 513,620 to Phillips, that a tube sheet could be formed with protruding nipples or bosses surrounding the tube holes to increase the area of contact between tubes the tube sheet. In this manner, a thinner tube sheet could be utilized to provide the same sealing relationship as one formed from thicker stock. This basic concept has been expanded upon over the years and refined by various heat exchanger designers, such as in U.S. Pat. No. 4,159,741 to Nonnenmann et al. and in U.S. Pat. No. 4,316,503 to Kurachi et al. In both Nonnenmann et al. '741 and Kurachi et al. '503, the nipples or flanges formed in the tube sheet have very specific configurations for providing an improved seal against the inserted tubes to permit the solderless sealing of the tube in the tubesheet hole. Solderless sealing may be accomplished by the internal expansion of the tube after it has been inserted into the tubesheet hole and is particularly useful in the art of making automobile radiators utilizing relatively thin gauge copper or brass.
Like heat exchangers, combustion chambers or fire boxes have many uses, such as in kilns and furnaces, and have been the subject of various designs and proposals for improvement. U.S. Pat. No. 4,889,061 to McPherson et al., discloses a refractory lined burning pit for incinerating waste materials. The pit liner includes a framework of structural steel to which is fastened a plurality of refractory panels. In Schiferi, U.S. Pat. No. 4,809,622, a slot forge is formed from a plurality of elongated insulation logs held in place by a supporting framework. In Yamaguchi, U.S. Pat. No. 5,122,055, a kiln is described that utilizes vertical and horizontal framing members. The outer plates of the kiln are clamped to the framework by plates that permit thermal expansion to take place without effecting the overall length of the kiln.
U.S. Pat. No. 4,011,394 to Shelley discloses a kiln construction employing an adjustable tie bar for clamping multiple layers of a kiln wall together. U.S. Pat. No. 540,987 to Jones and U.S. Pat. No. 1,809,210 to McLimans each illustrate the old expedient of using metal buckstays to support furnace walls formed of masonry units. U.S. Pat. No. 4,852,324 to Page shows a variable angle corner support for supporting the corners formed by abutting refractory panels in, e.g., a furnace.
As with heat exchangers and combustion chambers, numerous burner assembly configurations are extant. For example, German Offenlegungschrift 2,310,968 illustrates a sheetmetal burner holder having the capacity to support a plurality of individual burner elements. Each of a plurality of apertures in the sheetmetal holder for connecting to a gas inlet port of a corresponding burner has diametrically opposed notches which may hold tabs projecting from the burner element. German Offenlegungschrift DE 3932-855-A1 diagrammatically shows a burner tube affixed to a pipe extending from a vertical surface. U.S. Pat. No. 3,501,258 to Vales discloses a more conventional arrangement wherein a plurality of individual gas burner tubes are supported on a framework.
Notwithstanding the substantial efforts that have been expended to produce more efficient and economical fluid heaters and to improve heat exchangers, fireboxes and burner assemblies, each of the foregoing still have attributes that are not desirable. For example, the conventional metal manifold units that are used in forming tube-type heat exchangers are heavy, expensive to manufacture, difficult to integrate into plastic piping systems due to different rates of thermal expansion, and impede fluid flow therethrough because of rough interior surfaces. Cast iron has been utilized in heat exchangers for economic reasons but when subjected to even mildly corrosive liquids oxidizes or dissolves. Traditional combustion chamber construction is generally unwieldy, requiring the use of cementious or other hardening fireproof sealers to seal the units composing the firebox. Known burner assemblies are typically complex and heavy employing multiple elements that are expensive to manufacture and assemble.
Accordingly, the present invention is directed to resolving the aforementioned limitations that one would encounter in conventional fluid heaters and their constituent components.